Purging arrangement for refrigeration systems

ABSTRACT

A purging arrangement for a refrigeration system operable to remove noncondensable gases mixed with refrigerant vapor and water vapor from the system to condense the water and refrigerant constituents, to separate condensed refrigerant vapor from condensed water vapor, and to recover a substantial amount of the condensed refrigerant vapor while venting the remaining noncondensables to the atmosphere. The arrangement includes a heat exchanger in which the mixture of noncondensable gases, refrigerant vapor, and water vapor is passed in heat transfer relation with liquid refrigerant to separate the noncondensable gases from the condensable constituents, refrigerant vapor and water vapor, by condensing the latter. The condensed refrigerant vapor is thereafter separated from the condensed water vapor. The noncondensable gases are discharged from the heat exchanger when a predetermined pressure differential exists between the heat exchanger and the condenser of the refrigeration system. Flow of the mixture from the system to the heat exchanger is prevented while the noncondensable gases are being discharged from the heat exchanger.

United States Patent I r 13,592,017

[72] Inventors Martin H. Lipman; Primary Examiner-William .l. Wye

Harland E. Rex, both 01 Dewitt, N.Y. Atlomeysl-1arry G. Martin, Jr. and J. Raymond Curtin [211 Appl. No. 863,134 {22] Filed Oct. 2, 1969 [45} Patented July 13,1971 ABSTRACT: A purging arrangement for a refrigeration [73] Assignee Carrier Corporation system operable to remove noncondensable gases mixed with Syracuse, N Y, refrigerant vapor and water vapor from the system to condense the water and refrigerant constituents, to separate condensed refrigerant vapor from condensed water vapor, and to recover a substantial amount of the condensed refrigerant vapor while venting the remaining noneondensables to the at- [54] PURGING ARRANGEMENT FOR REFRIGERATION SYSTEMS 7 Claims, 2 Drawing 18$ mo sphere. The arrangement includes a heat exchanger 111 which the mlxture of noncondensable gases, refrigerant vapor, [52] US. Cl 2/85, and water vapor is passed in heat transfer relation with liquid 62/195, 62/47 refrigerant to separate the noncondensable gases from the [51] lllfi. CI F25!) 47/09 eondensable constituents refrigerant vapor and water vapor, [50] Fild ofSearch 62/85, 195, by condensing the latter The condensed refrigerant vapor is 474 thereafter separated from the condensed water vapor. The noncondensable gases are discharged from the heat exchanger [56] Rem-ewes cued when a predetermined pressure differential exists between the UNITED STATES PATENTS heat exchanger and the condenser of the refrigeration system. 2,986,894 6/ 1961 Endress 62/85 Flow of the mixture from the system to the heat exchanger is 3,013,404 12/1961 Endress 62/85 prevented while the noncondensable gases are being 3,145,544 8/ 1964 Weller 62/85 discharged from the heat exchanger.

PATENTEU JUL 1 3 197:

SHEET 1 0F 2 m wu u n i I r mm .Nm 8 R a mm! .2 S N g a 2 v E m om E m INVENTORS MARTlN H, LIPMAN HARLAND E. REX

ll j ATTHRNFY PATENTEU JUL 1 3 l97l SHEEI 2 0F 2 INVENTORS. MARTIN H. LIPMAN HARLAND E.REX

PURGING ARRANGEMENT FOR REFRIGERATION SYSTEMS BACKGROUN D OF TH E INV ENTION This invention relates to a purge recovery arrangement for refrigeration systems and more particularly to an arrangement for removing noncondensable gases from a refrigeration system and recovering therefrom any refrigerant admixed therewith.

In refrigeration systems such as centrifugal and absorption refrigeration systems with time, air, water vapor, and other gases gradually leak into or are formed in the system. This, as is to be expected, results in a malfunctioning of the system since noncondensable gases, for example, interfere with the heat exchange relation between the refrigerant and the condensing or the cooled medium, reducing the capacity of the machine.

A variety of systems have been evolved, designed to purge this foreign matter from a refrigeration system and to facilitate recovery of any refrigerant removed with said foreign matter. For example, some devices have employed an auxiliary compression refrigeration system for initiating flow of the noncondensable gases from the primary refrigeration system and for chilling and condensing the condensable vapors admixed with the noncondensable gases. The increased cost of manufacture and subsequent increase in maintenance arising from employing an additional compressor is obvious. Other systems, for example, have employed steam and water ejectors which do not permit recovery of the refrigerant.

The present invention provides an arrangement which permits purging of a refrigeration system to remove noncondensable gases and foreign matter from the refrigeration system, and thereafter to separate any purged refrigerant from the foreign matter and permit return of the refrigerant to the refrigeration system, thus assuring that loss of refrigerant due to the necessary purging operation is maintained at a minimum.

SUMMARY OF THE INVENTION This invention relates to a purging arrangement for a refrigeration system operable to remove noncondensable gases mixed with refrigerant vapor and water vapor from the system to condense the water and refrigerant constituents, to separate condensed refrigerant vapor from condensed water vapor, and to recover substantially all of the condensed refrigerant vapor and to return same to the refrigeration system.

The purging arrangement of this invention comprises a heat exchanger to which the mixture of noncondensable gases, refrigerant vapor, and water vapor is supplied from the condenser of the refrigeration system. The mixture is passed in heat transfer relation with a heat exchange medium, preferably with liquid refrigerant from the refrigeration system, whereby the condensable refrigerant vapors and water vapors are separated from the noncondensable gases. The noncondensable gases are discharged from the heat exchanger when a predetermined pressure differential exists between the heat exchanger and the condenser of the refrigeration system, the pressure differential being of a magnitude indicating the presence of an abnormal volume of noncondensables.

The condensed refrigerant vapor is separated from the condensed water vapor before being returned to the refrigeration system.

To prevent the discharge of a substantial volume of refrigerant gas during the discharge of noncondensable gases from the heat exchanger, means are provided to stop the flow of the mixture of noncondensable gases, refrigerant vapor, and water vapor from the condenser to the heat exchanger during such time.

The invention herein disclosed additionally includes a safety switch responsive to the temperature of the liquid formed in the heat exchanger. The switch will prevent the discharge of the noncondensable gases if the temperature of the liquid in the heat exchanger exceeds a predetermined point, even though the predetermined pressure differential exists between the condenser and the heat exchanger. The temperature responsive safety switch will prevent the noncondensable gases from being discharged at times when the temperature in the heat exchanger is too high to condense substantially the total refrigerant vapor entrained in the gaseous mixture previously described, and a substantial quantity of refrigerant gas would be lost due to its remaining admixed with the noncondensable gases discharged from the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically represents the purge arrangement of this invention; and V F IG. 2 illustrates schematically the control for the invention of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and more particularly to FIG. 1 thereof, there is shown a schematic view of a purge arrangement in accordance with the invention herein disclosed, as applied to a centrifugal refrigeration system 10. It should be understood that the invention may be utilized with other types of refrigeration systems such as systems employing a reciprocating compressor, or with absorption-type refrigeration systems.

Refrigeration system 10 comprises a compressor 11, a condenser 12 is having condenser sump 13 leading to an economizer 14 which supplies liquid refrigerant to evaporator or cooler 15, liquid refrigerant formed in condenser 12 flashcooled in the economizer 14, the flashed vapor being forwarded to the second stage of compression of compressor 11 through line 14', as shown in US. Pat. No. 2,277,647 issued Mar. 24, I942, Walter Jones, inventor. In cooler [5, liquid refrigerant is placed in heat transfer relation with a medium to be cooled, such as water. The vaporous refrigerant formed by the extraction of heat from the water is forwarded through line 16 to the first stage of compression of compressor 11.

From the upper part of condenser 12, a purge line 18 having a normally open valve 19, a restricting orifice 20, and line valves 21 and 22 is extended to an auxiliary heat exchanger 23. Purge line 18 includes a branch line 18' having trap 24. Branch line 18' is extended to economizer 14 for a reason to be more full explained hereinafter.

Auxiliary heat exchanger 23 is formed by a shell or casing 25. A heat exchange coil 26 is housed within casing 25 and is adapted to receive a relatively cold medium for passage therethrough. In the preferred embodiment, the cold medium is liquid refrigerant supplied from condenser 12 of the system 10 via line 27. Supply line 27 includes normally closed solenoid valve 28 and expansions device 29, shown as a handoperated expansion valve. It should be understood that other well-known expansion devices may be employed in lieu of the device shown.

The liquid refrigerant flows through coil 26 in heat transfer relation with a mixture of noncondensable gases, refrigerant vapor, and water vapor, passing over the outer surface of the coil, the gaseous mixture having been supplied to heat exchanger 23 via purge line 18. The refrigerant vapor and water vapor of the gaseous mixture are condensed and thereby separated from the noncondensable gases. The refrigerant having passed through coil 26 is delivered to the evaporator 15 via line 30.

Atmospheric line 41 leads from heat exchanger 23 and is provided with a normally closed solenoid valve 42, operable to control discharge of the noncondensable gases which collect in the heat exchanger. Control of valve 42 will be explained hereinafter.

As noted hereinbefore, one of the primary objects of this invention is the recovery of a substantial part of the refrigerant gas included in the gaseous mixtu're purged from the condenser 12. It has been found that the amount of refrigerant lost due to purging is substantially reduced by lowering the condensing temperature in the auxiliary condenser substantially below freezing. In the preferred embodiment, expansion device 29 is set to maintain a temperature of F. in condenser 23. Thus, it is apparent that the condensed water vapor does not form a liquid but, rather, forms crystals of ice.

A sump 311 connected to the bottom of condenser 23 receives the liquid refrigerant and ice crystals formed in the condenser. The ice crystals, being less dense than the liquid refrigerant, float on the refrigerant.

The liquid refrigerant and segregated ice crystals leave the sump 31 via relatively large diameter conduit 32. Conduit 32 is sized so the velocity of the refrigerant and ice crystals therethrough is relatively low, thereby streamline flow conditions are maintained to continue the separation of ice crystals from liquid refrigerant. Large diameter conduit 32 is led to a tee 33 of equally large diameter. Tee 33 functions as a weir to separate the crystals of ice from the liquid refrigerant. The ice crystals leave the tee 33 via the top conduit 35 connected thereto, while the liquid refrigerant exists from the tee via lower conduit 34.

Top conduit 35 delivers the ice crystals to an uninsulated dehydrator 36. The ice crystals eventually melt in dehydrator 36, and the moisture formed thereby is absorbed by the desiccant disposed in the dehydrator.

Liquid refrigerant flowing in conduit 34 is led to a second uninsulated dehydrator 37 to remove any moisture not separated by tee 33. Additionally, the inlet of dehydrator 37 is connected to the outlet of dehydrator 36 via line 38. Any liquid refrigerant passing with water through dehydrator 36 is led via line 38 to the inlet of dehydrator 37 where it mixes with the main body of liquid refrigerant.

The liquid refrigerant exiting from dehydrator 37 is essentiallymoisture-free and is returned to the refrigeration system via conduit 39 connected to evaporator 15. The flow of refrigerant through conduit 39 is controlled by normally closed valve 40. The opening of valve 40 is controlled by the level of the liquid refrigerant and ice crystals in sump 3ll in a manner to be more fully explained.

Connected to sump 33 via line 43 is float controller 4 8. The level of liquid in float controller 44 will rise at the level of fluid in sump 3ll rises and will fall as the level of fluid in sump 31 falls. The level sensing element 414' in float controller 44 is connected to a valve 70 controlling the opening and closing of an orifice 71 in the controller 414%. If sensing element M detects a rising level in sump 3i, it will actuate valve 70 to close orifice 71. If sensing element M detects a falling level in sump 31, it will actuate the valve to open the orifice.

Connected to controller 44 upstream" of the orifice and valve is conduit 45. Conduit 45 communicates the controller 44 with heat exchanger 23, thereby making the upstream" side of the orifice responsive to the pressure in heat exchanger 23. When the orifice is open due to the fall in the liquid level in the sump 31 as sensed by the level sensing element in the controller 44, line M is placed in communication with the upstream side of the orifice.

Line 46 communicates with control valve 40. The valve is maintained closed when there is sufficient pressure in line 46 due to the orifice in the controller 4% being open. When the orifice is closed due to a rise in the liquid level in sump 31, control valve Ml opens, thereby returning the liquid refrigerant to the system as previously described. 3

Now referring to FIG. 2, there is shown a preferred embodiment of a control for the purging arrangement of FIG. ll. In referring to the drawing, like numerals shall refer to like parts. Although the preferred embodiment of the control is shown as an electropneumatic system, it should be understood that a completely electrical or a completely pneumatic system may be utilized without departing from the scope of this invention.

The electrical components of the control are operated by a source of power represented by L and L The pneumatically operated components are actuated by compressed air supplied from a source not shown.

The control disclosed in FIG. 2 includes a first normally open switch 56. Switch 56 is controlled by pressure-actuated mechanism 57. The mechanism is responsive to the pressures in the condenser l2 and evaporator 15 of the system It). The mechanism illustrated schematically is comprised of an outer shell 57. Disposed within shell 57' is a diaphragm 62 extending horizontally so the interior of the shell is divided into an upper space and a lower space. A compression spring 63 is placed in the upper space of mechanism 57. Line 58 connects the upper space of mechanism 57 with the evaporator 15 so the top surface of the diaphragm 62 is responsive to evaporator pressure. Line 59 communicates the lower space of mechanism 57 with condenser 12 so the bottom surface of diaphragm 62 is responsive to condenser pressure. It is readily apparent that switch 56 will be closed when a predetermined pressure differential exists between the evaporator pressure and the condenser pressure. Compression spring 63 is utilized to obtain the desired pressure differential. Preferably, switch 56 will close when a pressure differential of 32 p.s.i. is reached and will open at a pressure differential of 24 p.s.i. The closing of switch 56 indicates the refrigeration system is in operation and purging may be required.

In series with switch 56 is a normally closed switch 51. Switch SI is similarly responsive to a predetermined pressure differential. Controlling the operation of switch Sll is mechanism 50, including shell 50 and diaphragm 64, which separates the shell into an upper and a lower chamber. Line 52 communicates the upper chamber of mechanism 50 with heat exchanger 23 so the top surface of diaphragm 64 is responsive to the pressure in the heat exchanger. Line 53 connects the lower chamber of mechanism 50 with condenser ll2 so the bottom surface of diaphragm 642 is responsive to condenser pressure. Switch 51 will be closed as long as a predetermined pressure differential exists between heat exchanger 23 and condenser 12, for example an 8 p.s.i. differential, and is designed to open when the predetermined differential has been exceeded. Compression spring 65 establishes the desired operating range for switch 51.

In series with the two switches described above is a second normally closed switch 60. Switch 60 is thermally responsive. The temperature sensing element 61 of switch so is placed in sump 31 to sense the temperature of the liquid being condensed. If the temperature of the condensed liquid exceeds a predetermined point, thermal switch 60 opens for a reason to be more fully explained hereinafter.

Connected in series with the three switches heretofore described is normally closed solenoid valve 54%. Valve 54 is disposed in compressed air supply line 55. Closure of the three switches during operation of the system 10 will actuate the valve. The opening of valve 54 communicates normally open valve 19 and normally closed valve 42 with the source of compressed air, closing valve 19 and opening valve 62. When valve 119 is closed, the supply of gaseous mixture from condenser 1l2 to heat exchanger 23 is interrupted. The opening of valve 42 communicates the heat exchanger 23 being with the atmosphere, the noncondensable gases in heat exchanger 23 being thereby discharged to the atmosphere.

Connected in series with switch 56 is refrigerant liquid supply valve 28 in line 27. The valve is solenoid actuatedv When switch 56 closes, valve 28 is opened, thereby supplying liquid refrigerant for heat exchange purposes to heat exchanger 23.

OPERATION The novel purge-recovery arrangement above disclosed is employed preferably in connection with the condenser of a centrifugal refrigeration system in which during operation, condensing pressure is generally above atmospheric pressure. The primary function of the purge-recovery arrangement is to move noncondensable gases and water from the refrigeration system and to recover most of the refrigerant admixed with the noncondensable gases and water vapor which is purged from the condenser.

The noncondensable gases tend to accumulate at the top of condenser 12 and when removed from the condenser through purge line 18, carry refrigerant vapor and water vapor, if any, therewith. When system is in operation, a pressure differential between condenser 12 and heat exchanger 23 is established. The greater pressure in condenser 12 forces the gaseous mixture through line 18, normally open valve 19, ori lice 20, line valves 21 and 22 to heat exchanger 23. Branch line 18 and trap 24 are preferably installed to separate any refrigerant condensing in line 18 from the gaseous mixture proceeding to heat exchanger 23. Branch line 18' returns the condensed refrigerant to economizer 14. The condensable vapors of the gaseous mixture are condensed by passing over the coil 26 in heat transfer relation with the liquid refrigerant flowing therethrough. The liquid refrigerant has been supplied from condenser 12 through line 27, normally closed valve 28 having been opened by the closing of switch 56 in response to the startup of system 10. Expansion valve 29 regulates the supply of refrigerant to coil 26 to obtain the desired condensing temperature for maximum refrigerant recovery.

The noncondensable gases collect at the top of heat exchanger 23 and may be released to the atmosphere through line 41. The condensed refrigerant vapor and condensed water vapor in the form of ice crystals collect in sump 31, the lighter ice crystals floating on top of the heavier liquid refrigerant.

The segregated ice crystals and liquid refrigerant leave sump 31 to be separated as heretofore explained. The liquid refrigerant is returned to the refrigeration system when valve 40 is opened in response to the rising level of liquid in sump 31.

The controls for the purge arrangement permit automatic operation of the purge unit and in addition, include safety switches, operable to prevent purging at time when a substantial volume of entrained refrigerant gas would be lost if noncondensable were discharged from heat exchanger 23.

During normal operation of refrigeration l0, switch 56 is closed in response to the minimum pressure differential between evaporator and condenser 12 being obtained. Closure of switch 56 energizes valve 28, thereby supplying liquid refrigerant to coil 26 of heat exchanger 23.

At startup and for a period of time thereafter, normally closed switch 51 is open due to the pressure differential between condenser 12 and heat exchanger 23 being in excess of the predetermined point. With switch 51 open, valve 54 is in its normally closed position, preventing compressed air from being supplied to valves 19 and 42. Thus, valve 19 is in its normally open position and the purged gaseous mixture flows to heat exchanger 23. Valve 42 is in its normally closed position, preventing discharge of noncondensable gases to the atmosphere. As noncondensables are accumulated in heat exchanger 23, the pressure therein will rise and eventually the predetermined pressure differential between condenser 12 and heat exchanger 23 will be attained to close switch 51. The closure of switch 51 actuates valve 54, thereby communicating the source of compressed air with valves 19 and 42 through line 55.

The compressed air operates to close valve 19 and to open valve 42. The opening of valve 42 communicates heat exchanger 23 with the atmosphere to discharge the noncondensable gases therefrom. The simultaneous closing of valve 19 prevents the gaseous mixture from flowing to heat exchanger 23 while the noncondensable gases are being discharged. The interruption of the flow of the gaseous mixture operates to prevent a relatively substantial loss of entrained refrigerant gas which otherwise would be blown out to the atmosphere before it might be condensed in heat exchanger 23. After sufficient noncondensable gases have been discharged to increase the pressure differential between condenser 12 and heat exchanger 23, switch 51 opens and the purge cycle recommences. Thermally operated, normally closed switch 60 acts as a safety device. lfthe condensing temperature were to be too high, for example, liquid supply valve 28 might become clogged, a substantial amount of refrigerant would not be condensed and would be lost when valve 42 opens in response to the accumulation of noncondensables in heat exchanger 23. Opening of switch 60, in response to a predetermined condensing temperature being exceeded,

prevents the actuation of valve 54 even though the predetermined pressure differential has been obtained to close switch The present invention provides a novel purge-recovery arrangement for use in removing noncondensable gases and water vapor from the refrigerant of refrigeration systems. Additionally, the invention provides means operable to obtain the substantial recovery of any refrigerant that has been admixed with the gaseous mixture removed from the refrigeration system and thereafter separated therefrom The arrangement functions automatically and is extremely efficient in operation in the amount of refrigerant recovered.

The above disclosure has been give by way of illustration and elucidation, and not by way of limitation, and it is desired to protect all embodiments of the disclosed inventive concept within the scope of the appended claims.

We claim:

1. A purging arrangement for a refrigeration system including a compressor, a condenser, an evaporator, and expansion means, said arrangement being operable to purge noncondensable gases from the system and to recover refrigerant mixed with the noncondensable gases comprising:

a. a heat exchanger;

b. first conduit means connecting said heat exchanger with said condenser for the flow of said noncondensable gases and entrained vapor to said heat exchanger from said condenser;

. second conduit means connected to said heat exchanger to supply a heat exchange medium to said heat exchanger, said heat exchange medium passing in heat transfer relation with said noncondensable gases to condense said entrained vapor carried by said noncondensable gases, thus separating said entrained vapor from said noncondensable gases, said entrained vapor including refrigerant vapor and water vapor;

d. means to separate the condensed refrigerant vapor from said condensed water vapor;

e. means to return said condensed refrigerant vapor to said refrigeration system;

f. means governing release of noncondensable gases from the heat exchanger, said governing means including a line connecting the heat exchanger with ambient atmosphere, a valve in said line governing passage of said gases through said line and a control for said valve including a member responsive to a predetermined pressure differential between condenser and heat exchanger pressure to actuate said valve to permit discharge of said noncondensable gases from said heat exchanger; and

g. means responsive to the actuation of said noncondensable gases discharge valve to prevent flow of said noncondensable gases from said condenser to said heat exchanger.

2. A purging arrangement in accordance with claim 1 wherein said means responsive to the actuation of said noncondensable gases discharge valve includes a normally open valve in said first conduit means, said normally open valve being closed upon actuation of said discharge valve.

3. A purging arrangement in accordance with claim 2 further including:

means responsive to a predetermined temperature condition in said heat exchanger to prevent said discharge valve from being actuated even though said predetermined pressure differential has been reached.

4. A purging arrangement in accordance with claim 3 wherein said separating means includes at least one dehydra- 10X.

5. A purging arrangement in accordance with claim I further including:

means responsive to a predetermined temperature condition in said heat exchanger to prevent said discharge valve from being actuated even though said predetermined pressure differential has been reached.

6. A method of purging a refrigeration system to remove noncondensable gases and water vapor from the refrigerant of I the system and to recover refrigerant vapor mixed with the noncondensable gases and water vapor comprising the steps of:

a. collecting the mixture of noncondensable gases, water vapor and refrigerant vapor in a first portion of the system;

b. removing the mixture to a second portion of the system;

c. passing a heat exchange medium in heat transfer relation with the mixture in the second portion of the system to separate condensable vapors from the noncondensable gases;

d. separating the condensed refrigerant vapor from the condensed water vapor;

e. returning the condensed refrigerant to the system;

f. discharging the noncondensable gases from the second portion of the system when a predetermined pressure differential between the first portion of the system and the second portion of the system is reached; and

g. preventing flow of the mixture from the first portion of the system to the second portion of the system when the noncondensable gases are being discharged from the second portion of the system.

7. The method of purging a refrigeration system in accordance with claim 6 further comprising the step of:

preventing the discharge of noncondensable gases from the second portion of the system even though the predetermined pressure differential has been reached, when a predetermined temperature condition exists in the second portion of the system. 

1. A purging arrangement for a refrigeration system including a compressor, a condenser, an evaporator, and expansion means, said arrangement being operable to purge noncondensable gases from the system and to recover refrigerant mixed with the noncondensable gases comprising: a. a heat exchanger; b. first conduit means connecting said heat exchanger with said condenser for the flow of said noncondensable gases and entrained vapor to said heat exchanger from said condenser; c. second conduit means connected to said heat exchanger to supply a heat exchange medium to said heat exchanger, said heat exchange medium passing in heat transfer relation with said noncondensable gases to condense said entrained vapor carried by said noncondensable gases, thus separating said entrained vapor from said noncondensable Gases, said entrained vapor including refrigerant vapor and water vapor; d. means to separate the condensed refrigerant vapor from said condensed water vapor; e. means to return said condensed refrigerant vapor to said refrigeration system; f. means governing release of noncondensable gases from the heat exchanger, said governing means including a line connecting the heat exchanger with ambient atmosphere, a valve in said line governing passage of said gases through said line and a control for said valve including a member responsive to a predetermined pressure differential between condenser and heat exchanger pressure to actuate said valve to permit discharge of said noncondensable gases from said heat exchanger; and g. means responsive to the actuation of said noncondensable gases discharge valve to prevent flow of said noncondensable gases from said condenser to said heat exchanger.
 2. A purging arrangement in accordance with claim 1 wherein said means responsive to the actuation of said noncondensable gases discharge valve includes a normally open valve in said first conduit means, said normally open valve being closed upon actuation of said discharge valve.
 3. A purging arrangement in accordance with claim 2 further including: means responsive to a predetermined temperature condition in said heat exchanger to prevent said discharge valve from being actuated even though said predetermined pressure differential has been reached.
 4. A purging arrangement in accordance with claim 3 wherein said separating means includes at least one dehydrator.
 5. A purging arrangement in accordance with claim 1 further including: means responsive to a predetermined temperature condition in said heat exchanger to prevent said discharge valve from being actuated even though said predetermined pressure differential has been reached.
 6. A method of purging a refrigeration system to remove noncondensable gases and water vapor from the refrigerant of the system and to recover refrigerant vapor mixed with the noncondensable gases and water vapor comprising the steps of: a. collecting the mixture of noncondensable gases, water vapor and refrigerant vapor in a first portion of the system; b. removing the mixture to a second portion of the system; c. passing a heat exchange medium in heat transfer relation with the mixture in the second portion of the system to separate condensable vapors from the noncondensable gases; d. separating the condensed refrigerant vapor from the condensed water vapor; e. returning the condensed refrigerant to the system; f. discharging the noncondensable gases from the second portion of the system when a predetermined pressure differential between the first portion of the system and the second portion of the system is reached; and g. preventing flow of the mixture from the first portion of the system to the second portion of the system when the noncondensable gases are being discharged from the second portion of the system.
 7. The method of purging a refrigeration system in accordance with claim 6 further comprising the step of: preventing the discharge of noncondensable gases from the second portion of the system even though the predetermined pressure differential has been reached, when a predetermined temperature condition exists in the second portion of the system. 